Journal of ethnopharmacology · 2025
Uncaria attenuata and its main corynanthean alkaloid, villocarine A, exert antinociceptive effects in rats via activation of central μ-opioid receptors.
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Ching-Ga Tan Ai Fein, Chear Nelson Jeng-Yeou, Ahad Mohamad Anuar, Khor Boon-Keat, León Francisco, Sharma Abhisheak, Seabra Maria Abl, Tan Wen-Nee, Hassan Zurina, Murugaiyah Vikneswaran, McCurdy Christopher R, Ramanathan Surash
Аннотация
ETHNOPHARMACOLOGICAL RELEVANCE: Uncaria plants (Rubiaceae) are traditionally used to treat various CNS disorders, including pain and drug addiction. In Southeast Asia, Uncaria plants are also used as a substitute for kratom (Mitragyna speciosa).
AIM OF THE STUDY: This study was designed to investigate the opioid analgesic activity of Uncaria attenuata (UA) methanol extract, total alkaloid extract, and the main alkaloid - villocarine A.
MATERIALS AND METHODS: The antinociceptive activity of UA methanol extract at doses of 250 and 500 mg/kg, as well as the total alkaloid extract at 50 and 100 mg/kg, and villocarine A at 5, 10, and 20 mg/kg, was evaluated orally in healthy male Sprague Dawley rats using a hot plate model. Morphine and mitragynine were used as positive controls. The extracts were also analyzed for their villocarine A content using a validated HPLC-DAD method. The involvement of central opioid receptors in the antinociceptive effects induced by UA extracts and villocarine A was further confirmed through an in vivo naloxone antagonism test and an in vitro radioligand binding assay.
RESULTS: The UA methanol extract (500 mg/kg) and alkaloid extract (100 mg/kg) significantly reduced pain sensation in rats (P < 0.05) in the hot-plate model. Villocarine A (20 mg/kg, p.o.) also significantly reduced pain, with an effect comparable to morphine (5 mg/kg, i.p.) and superior to mitragynine (20 mg/kg, p.o.). The antinociceptive effects of UA alkaloid extract and villocarine A were all blocked by naloxone (2 mg/kg, i.p.), a non-selective opioid receptor antagonist. The receptor-radioligand binding assay further demonstrated that both UA alkaloid extract and villocarine A bound to μ-opioid receptors (Ki = 872 ng/mL; 944 nM, respectively). HPLC analysis revealed that the UA methanol and alkaloid extracts contained approximately 3 % and 25 % (w/w) of villocarine A, respectively.
CONCLUSION: The UA methanol extract and its alkaloid-enriched extract, and villocarine A exhibited significant opioid analgesic effects in animal and in vitro models. This study supports the potential use of Uncaria species as a pain reliever as well as an alternative to kratom.
AIM OF THE STUDY: This study was designed to investigate the opioid analgesic activity of Uncaria attenuata (UA) methanol extract, total alkaloid extract, and the main alkaloid - villocarine A.
MATERIALS AND METHODS: The antinociceptive activity of UA methanol extract at doses of 250 and 500 mg/kg, as well as the total alkaloid extract at 50 and 100 mg/kg, and villocarine A at 5, 10, and 20 mg/kg, was evaluated orally in healthy male Sprague Dawley rats using a hot plate model. Morphine and mitragynine were used as positive controls. The extracts were also analyzed for their villocarine A content using a validated HPLC-DAD method. The involvement of central opioid receptors in the antinociceptive effects induced by UA extracts and villocarine A was further confirmed through an in vivo naloxone antagonism test and an in vitro radioligand binding assay.
RESULTS: The UA methanol extract (500 mg/kg) and alkaloid extract (100 mg/kg) significantly reduced pain sensation in rats (P < 0.05) in the hot-plate model. Villocarine A (20 mg/kg, p.o.) also significantly reduced pain, with an effect comparable to morphine (5 mg/kg, i.p.) and superior to mitragynine (20 mg/kg, p.o.). The antinociceptive effects of UA alkaloid extract and villocarine A were all blocked by naloxone (2 mg/kg, i.p.), a non-selective opioid receptor antagonist. The receptor-radioligand binding assay further demonstrated that both UA alkaloid extract and villocarine A bound to μ-opioid receptors (Ki = 872 ng/mL; 944 nM, respectively). HPLC analysis revealed that the UA methanol and alkaloid extracts contained approximately 3 % and 25 % (w/w) of villocarine A, respectively.
CONCLUSION: The UA methanol extract and its alkaloid-enriched extract, and villocarine A exhibited significant opioid analgesic effects in animal and in vitro models. This study supports the potential use of Uncaria species as a pain reliever as well as an alternative to kratom.